NEW YORK (Reuters Health) - A new study finds suicide rates for female teens and preteens in Canada rose over the past few decades while the overall number of kids who took their own lives was dropping.

Researchers with Canada's public health agency also noted a change in the youngsters' favored methods of suicide - from guns or poisons, to suffocation by strangulation -- though they can't explain either pattern.

"Our message is that all suicide is a tragedy and the trend is very disturbing," said the study's lead author, Robin Skinner, an epidemiologist with the Public Health Agency of Canada in Ottawa.

Overall, suicide is the second leading cause of death for Canadians between 10 and 19 years old, after accidental injuries.

Skinner told Reuters Health that they saw a slight improvement in the suicide rates for all Canadians in that age group between 1980 and 2008. Whereas 6.2 of every 100,000 young Canadians killed themselves in 1980, the rate fell to 5.2 per 100,000 in 2008.

In general, there was about a 1 percent annual decline over nearly three decades.

But, Skinner said, they wanted to look deeper.

When they did, the group found there was no significant change in suicide rates for boys 10 to 14 years old. In 2008, 1.6 per 100,000 committed suicide.

However, the rate of suicide among boys between ages 15 and 19 fell considerably. In 1980, 19 per 100,000 boys in that age group took their own lives compared to 12.1 per 100,000 in 2008.

Though girls had much lower suicide rates than boys, they trended in the opposite direction.

In 1980, 0.6 per 100,000 girls between ages 10 and 14 committed suicide. That number increased to 0.9 per 100,000 in 2008.

Among girls 15 to 19 years old, the suicide rate rose from 3.7 per 100,000 in 1980 to 6.2 per 100,000 in 2008.

The study did not examine why the rates for girls increased over the 28-year period, or why that of boys dropped.

But the researchers do point out a fairly steady rise among both boys and girls in deaths by suffocation, along with a fall in deaths by poisoning or firearms.

In 1980, 140 young Canadians used a firearm to kill themselves, 60 used poison and 74 used a form of suffocation. In 2008, those numbers were 22, 20 and 177, respectively.

Previous research has found that young people perceive hanging to be a "clean, quick and painless method" of suicide, according to the authors.

In addition, they write, a so-called "choking game" has grown in popularity among kids and teens during the study period. It involves either strangling the throat or applying pressure to the chest to achieve euphoria from oxygen deprivation.

"The 'game' can turn deadly if the participant being choked is physiologically susceptible or if the pressure is not released quickly enough after the loss of consciousness. Deaths resulting from the 'choking game' have the potential to be misclassified as suicides, especially when the "game" is played alone," Skinner's team writes in the Canadian Medical Association Journal.

He told Reuters Health, however, that although suicides -- especially non-violent deaths -- can sometimes be misclassified, past studies have shown suicide rates are still reliable.

A commentary by Dr. Laurence Kirmayer, of the Department of Psychiatry at McGill University in Montreal that accompanies the study suggests the increase in suicides among girls might be explained by the more lethal methods young Canadians are using to attempt suicide.

"Girls tended to use poisoning not gunshots; hanging is potentially more lethal than poisoning, partly because people often use sublethal doses of pills or other substances," Kirmayer told Reuters Health in an email.

The increasing popularity of suffocation by hanging is a trend Canada shares with the U.S., and might be explained by laws meant to keep guns away from children speculated one expert who was not involved in the study.

"It's very possible that young people who die by suicide in the U.S. are increasingly selecting hanging/suffocation as a method-specific substitution for firearms," wrote Jeff Bridge, of the Research Institute at Nationwide Children's Hospital in Columbus, Ohio, in an email.

But, Bridge, who's looked at suicide trends among U.S. youths, told Reuters Health that unlike Canada, the youth suicide rate in the U.S. has been much more volatile.

According to the National Institute of Mental Health, there were 0.9 per 100,000 suicides among Americans between the ages of 10 and 14 in 2007. That number was 6.9 per 100,000 for kids between the ages of 15 and 19 years old.

Kirmayer says "access to mental health care and reducing stigma may play a role" in preventing suicides. He adds, "Antidepressants may be part of that" but they are more suitable for severe and persistent depression "and may not be as effective (or appropriate) for some of the more acute, episodic, impulsive, crisis-based suicides seen among young people."

According to Bridge, the main message is that suicides are preventable deaths.

"We need to take an aggressive public health approach to suicide prevention in all young people and focus on approaches that prevent suicidal behavior before it ever occurs," he said.